Siemens–Not Just for Profibus Anymore

In PCS 7 We May Have the First SIL-Capable Logic Solver With Native Support for Foundation Fieldbus

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John RezabekBy John Rezabek, Contributing Editor

Some of us came to know Siemens as a process instrument manufacturer many years ago through its excellent line of continuous analyzers, for example, the "Ultramat" and "Oxymat" NDIR and paramagnetic O2 instruments. Through North American acquisitions like Milltronics, Moore Products and Applied Automation, Siemens' logo has been showing up on an increasing number and variety of process plant devices. However, Siemens PCS 7 (http://tinyurl.com/3n9elu2)—the powerful host system that aims to compete with DCS offerings from process-industry leaders such as Invensys, Emerson, ABB, Honeywell and Yokogawa—remains a little mysterious in the United States. There's a system inside the fence line where I work, controlling a Linde Hydrogen plant for a neighboring refinery. And there are Siemens systems all over the western hemisphere, some packaged with other Siemens offerings, some replacing aging APACS or Texas Instruments 500-series PLCs, and, of course, Siemens systems are abundant in the discrete manufacturing sector. But, for all Siemens' apparent ubiquity, I had to go to India to discover a pretty exciting new feature—support for Foundation fieldbus (FF).

Siemens was present in force at the Fieldbus Foundation's General Assembly in March 2011 with one of the largest booths, chock-a-block full of PCS 7 and fieldbus hardware. The PCS 7 platform has had some support for FF for awhile, but the current solution was introduced and marketed beginning in 2010. The foundation's website (www.fieldbus.org) says PCS 7 is a "registered host," passing all the requirements for a class 61a "integrated host"—the same as ABB, Honeywell, Invensys and Yokogawa.

One of Siemens' unique offerings is a redundant "ring" topology for H1 (the twisted-pair, basic physical layer of fieldbus), a feature originally developed for Profibus PA. The Siemens physical layer hardware is engineered to allow "live" expansion of the H1 segment with auto-termination. Similar to physical layer hardware offered by Moore-Hawke (www.miinet.com/products/sg_fieldbus.shtml), the need for a terminator is electronically sensed and added to the network where it's needed.

While "redundant ring" at the H1 segment level is not widely used in the large process industries, it's potentially groundbreaking for SIL-rated safety applications. In PCS 7, we may have the first SIL-capable logic solver with native support for Foundation fieldbus. While not the FF-SIF "black channel" support required for the highest safety-integrity levels, how much of a leap can it be to add this capability? PCS 7 has supported the "Profisafe" protocol for many years, but there have been few PA field devices introduced with the same capability, so applications have been scarce. FF's process-industry- laden end-user community has been clamoring for FF-SIF for some time, with "alpha" demonstration projects in labs at Shell, BP, Chevron and two at Saudi Aramco. Could Siemens be the power that finally vanquishes the chicken-and-egg syndrome that's slowed the introduction of FF-SIF products?

Aside from the analyzers with which I've been familiar for years, Siemens offers a fairly comprehensive repertoire of field devices, many of which are available as certified/"check marked" FF versions. Quite a few are manufactured in North America, and the line includes a positioner that's said to be one of the most popular in the world, the SIPART PS2. A zero-bleed design, it's the only intelligent positioner I've seen that offers diagnostics for plug and seat wear, deposits and clogging of the physical valve itself. The more common diagnostics for friction/"stiction" are included, as well as built-in partial-stroke testing for on-off applications. Also, thanks to its Milltronics heritage, Siemens offers some of the most advanced and capable ultrasonic and radar level instruments.

There are a lot of capable factory people on our side of the Atlantic, but the Siemens web site might need a tune-up to help me find my local rep! 

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